package dya07;

import java.util.Random;

/**
 * 需求:生成?位验证码(大写字母,小写字母,数字)
 */
public class VerificationCode {
    public static void main(String[] args) {
        String code = generateVeriCode(4);
            System.out.println("验证码:"+code);
    }

    public static String generateVeriCode(int len){
        String code = "";
        char[]chs ={'a','b','c','d','e','f','g','h','i','j','k','l','m',
                    'n','o','p','q','r','s','t','u','v','w','x','y','z',
                    'A','B','C','D','E','F','G','H','I','J','K','L','M',
                    'N', 'O','P','Q','R','S','T','U','V','W','X','Y','Z',
                    '1','2','3','4','5','6','7','8','9'};

        Random random = new Random();
        for (int i = 1; i <= len ; i++) {    //len次
            int index = random.nextInt(chs.length);//随机下标 以后用这种随机
            code += chs[index];             //获取随机字符并拼接到code中
        }
        /*过程:
            i=1     index=0     code="a"
            i=2     index=10    code="ak"
            i=3     index=61    code="ak9"
            i=4     index=28    code="ak9C"
            ...
            i=len
         */
        return code;
    }

}

        /*;
        for (int i = 1; i <= len; i++) {//len次
            int index = (int) (Math.random()* chs.length);//随机下标
            code += chs[index];//获取随机字符并拼接到code中
        }
         */
